1.x²-y²-x+1/4
=(x²-x+1/4)-y²
=(x-1/2)²-y²
=(x-y-1/2)*(x+y-1/2)
2.9m^2-n^2+3m-n
=(3m+n)(3m-n)+(3m-n)
=(3m-n)(3m+n+1)